Private branch exchange cord circuit providing warning tone when operator listens in



K. L. BURGENER PRIVATE BRANCH EXCHANGE CORD CIRCUIT PROVIDING July 29, 1952 WARNING TONE WHEN OPERATOR LISTENS IN Filed July l, 1948 om Do @moo Patented July 29, 1952 PRIVATE BRANCH' EXCHANGE CORD` CIR- CUIT PROVIDING WARNING TONE `WHEN' Y OPERATOR LISTENS IN f L i Karl L. Burgener, Villa Park, Ill., assignor tov Automatic Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application July 1, 1948, Serial No. 36,535 5 Claims. (Cl. 1791-51) The present invention relates to private branch Aexchange telephone systems and more particularly to improved switchboard apparatus for such systems.

' It is a general object of the present invention to provide in a private branch exchange or P. X telephone systems improved switchboard apparatus that is so connected and arranged VVthat whenever the operator telephone circuit at .the switchboard is connected into an established local or trunk connection, or whenever alocal or trunk connection is established including the operator telephone circuit, a distinct intrusion tone is applied to the established connection in order to warm the persons involved therein of vthe connection of the operator telephone cir cuit in the established connection.

' AAnother object of the invention is to provide a manual switchboard including a plurality of cord circuits, wherein the facility noted is incorporated in each of the cord circuits so that whenever the operator at the switchboard connects any'idle one of the cord circuits into an established connection that is completed via any other of the cord circuits, an intrusion tone is automatically applied via the one cord circuit to the established connection in the event the operator telephone circuit is connected to the one cord circuit. f

A further object of the invention is to provide an improved and exceedingly simple cord circuit embodying the facility noted.

Further features of the invention pertain Ato the particular arrangement of the circuit elcments of the system, whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and .method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing, in which the single figure illustrates the details of an automatic telephone system having incorporated therein the features of the present invention.

Referring now more particularly to the drawing, there is illustrated an automatic telephone system comprising a central oliicanot shown, anda private branch exchange or P. B. X I

interconnected by a plurality of trunks, includ- .ing the trunk II. nate in trunk circuits, not shown, in the central The trunks I I, etc. termioflice and in trunk circuits I2, etc., in the P. B. X I0. The central oflice may be of any suitable and the central ofce.

4 individual jacks J I3, etc., at the switchboard;

and the line circuits I6, 2|, etc., are terminated in individual jacks J l1, J22, etc., at the switchboard. Also the trunk circuits I2, etc., are provided with individual trunk lamps LM, etc., atthe switchboard; and the line circuits I 6, 2I, etc., are provided with individual line lampsLlS, L23, etc., at the switchboard. The switchboard may comprise a plurality ofoperatorpositions before which multiples ofthe trunk jacks JI3, etc.,-the trunk lamps LI4, etc., the line jacks JIT, ,122, etc., and the line lamps LIS, L23, etc., appear, so that the operator at any position at the switchboard may set up the various connectionsinvolving the lines in the P. B. X I0 and the trunks extending between the P. B; X Il! t Each operator position at the switchboard in the P. B. X IU may be provided with equipment identical to that illustrated that includes an operator telephone circuit 40, a tone circuit and a plurality of cord circuits 30, etc. The operator telephone circuit 4I] comprises a telephone instrument including a transmitter 4I, a receiver '42 and av repeating coil 45, including primary winding section 48 and 49, a secondary winding 41 and a tertiary winding 46; The tone circuit 60 comprises a relay network including a plurality of start relaysRG, etc. individual Yto the cordcircuits 30, etc.,. a tone relay R10, and `three controlrelays R80, R and R90. 1 ,40-

y calto the cord circuit 3l! that comprises a front ,Preferably, each of the cord circuits is identiplug PBI, a rearplug P32, a front supervisory lamp B33 associated with the front plug P3I and a rear supervisory lamp L34 associated with the rear plugP32; Also the cord circuit 30 comprises a ring station key X35, a ring trunk and station vkey Kat` and a talk key KST. Further the cord circuit 30 comprises a telephone rchannel between the front plug PSI and the rear plug P32 and av relay network including a ring relay RIM),

abattery supplyrelay RI I0, a sleeve relay RIZO,

.abattery supply lrelay RISO, a sleeve relayr DI40, a sleeve or control .relay R! 50, a series relay RI60 and a'ringrelay RI'IO.

In passing vtisnoted that when the operator 3 at the switchboard utilizes the cord circuit 30 to set up a telephone connection, the front plug P3I is always employed to answer a call on a line in the P. B. X I and that the rear plug P32 is always employed to extend the call to a line in the P. B. X I0 lor to a trunk extending between the P. B. X I0 and the central ofcef. Also when the operator at the switchboard utilizes the cord circuit 3B to set up a telephone connection, the rear plug P32 is always employed to answer a call on a trunk extending between the central o'ice and the P. B. X Ill; and that the front plug P3I is always employed to extend the c all to a v ply relay RI 3Q are connected via the contacts I2 I,

line in the P. B. X I0. This coordinated use of the front plug P3I and the rear plug P32 in the y cord circuit 30 is necessary since the cord circuit 30 constitutes a universal cord that may he employed for answering calls on both lines in the P. B. X I0 and on trunks extending between the central office and the P. B. X I0.

A better understanding of the connection and arrangement of vthe apparatus incorporated in the cor-d circuit 30 in conjunction with the associated equipment at the switchboard will be facilitatedfrom a consideration of the extension of the Various local and trunk calls involvingy the P. B. X I- and the central office.

First assuming that Va call is extended from the central ofce via the trunk II to the P. B. X

illfthe trunk circuit` I2 is governed to illuminate the trunk lamp L|4 in order to indicate the presence of the trunk call waiting to be answered. Now assuming that the operator at the position illustrated at the switchboard inthe P. B. X I0 is idle and is to answer the call, an idle cord cireuit,rsuch Vfor example, as the cord circuit 30 isselected and the rearplug P32 thereof is inserted in to the trunk jack JI3 extending to the trunk circuit I2, and the talk keyK3T is operated. When the talk key K3T is thus operated, there is completed, at the first and rsecond contacts thereof, a connection including the condenser I) -for bridging the primary winding sections 48 and 49 of the repeating coil 45 across the telephone channel in the c ord circuit'30, the transmitter 4| of the telephone instrument at Athe operator position illustrated is supplied with current'via the inductance element'43 and the secondary winding 41 of the repeating coil 45. Also when the talk key K3T is thus operated, thereis prepared, at the third contacts thereof, a circuit traced hereinafter for operating thestart relay R65vin the` tone circuit 60, which arrangement is utilizedfor a purpose more fully explained subsequently.

` When the rear plug P32 is-inserted into the trunk jack JI3, a circuit, including the sleeve of the trunk jack JI3, the sleeve of the rear plug P32 and the contacts |04, is completed'forenergizing the upper and lower windings of the control relay RI50 in series with the lower winding of the sleeve relay RMB; whereby the control relay R150 operates to complete, at the contacts |5I, a path for short-circuitingthe upper winding thereof. At this time, the control relay RISE) is retained in its operated position and the sleeve relay RMD operates. Also Vthe trunk circuit ,I2 is governed in order' to extinguish the trunk lamp LIV-4 indicating that the call on the trunk II has been answered at this time.l Upon operating the sleeve relay RI40 completes, at the contacts |42 and |43, a path, including the condenser |49, for connecting the upper winding O f the sleeve relay RIM! in series via the. upperV and lower windings of the battery supply relay RIS() across theV tele- |24 and the first and second contacts of the talk key -K3T and the condenser 5|) to the primary winding sections 48 and 49 of the repeating coil 45; whereby a telephone connection is completed at this time between the trunk I I and the operator telephone circuit 4D so that the operator at .extended to the telephone station TI in the P. B. X `II), the operator at the switchboard in the P. B. X IG inserts the iront plug P3I into the line jack JIT, assuming that the telephone station TI is idle at this time, as indicated by the extinguished line lamp LI8. When the front plug P3I is thus inserted into the line jack J IT, ground potential in the line circuit I6 is applied via the sleeve of the line jack JIT to the sleeveof the front plug P3I, thereby completing a circuit, including the contacts IGI, for illuminating the front, supervisory lamp L33 in order to indicate that the present callA has not been answered at this time.

The operator then operates the ring station key KES completing, at the second contacts thereof, a circuit for energizing the winding of the ring relay RITil in order to cause the latter relay tov operate shortly thereafter, it being of the slow-to-operate type. Upon operating the ring relay Rl'lil interrupts, at the contacts |TI and |14, the connection between the tip and the ring of the front plug P3I and the telephone channel in the cor-d circuit 3|); and completes, at the -contacts IT2- and |13, a path, including the first and third contacts of the ring front key X35, for connecting Aground potential and the ring conductor C respectively to the tip and the ring of the front plug P3I and consequently to the tip and the ring of the line jack JIT; whereby ringing current is projected over the line l5v to the telephone station TI operating the ringer thereat. The operator then restores the ring stationkey KSB in order to effect the restoration of the ring relay RlT. Upon restoring the ring relay RITE interrupts, at the contacts |72 and |T3, the path for projecting ringing current over the line I5; and recomplete's, at the contacts ITI and H4, the connection between the tip and the ring of the front plug P3I and the telephon channel in thecord circuit 30.

When the call is answered at the telephone station TI., a circuit, including the winding-.of the series relay RIGU, is completed for supplying battery current from the central office to the telephone instrument at the telephonev station TI; and a three-way telephone connection is completed involving the subscriber or operator at .the central ofce, the operator position illustrated Vat the switchboard and the telephone station TI.

-aeoases -cuit for illuminating the iront supervisory lamp L33 indicating that the call has been answered at the telephone stationTI. Also the series re- -lay R i60 completes, at the contacts |62, a circuit, including the grounded sleeve of the line jack J I1, the sleeve of the front plug PSI, the contacts I52 and |26 andthe third contacts `ci the operated talk key K31, for operating the start relay R65 in the tone circuit 66. The start relay R65 is operated at this time, since the telephone connection Ibetween the subscriber or operator in the central oi'lice and the telephone station TI in the P. B. X I0 includes the operator telephone circuit G0 at the switchboardin the P. B. X I0 as the telephone connection mentioned is not private since the operator at the position illustrated at the'switchboard may listen and converse therein.

Upon operating the start relay R65 completes, at the contacts 66, a circuit, including the contacts 1I, for energizing the upper winding of the tone relay R in order to cause the latter relay to operate. Upon operating the tone relay-R10 interrupts, atthe contacts 7l, the circuit Vfor energizing the upper winding thereof; whereby the tone relay R10 restores to recomplete, at the contacts 1 I, the circuit for .energizing the upper winding thereof. Accordingly, the ,tone relay R10 operates buzzer fashion; whereby a tone is induced in the lower winding thereof. Also upon `cperatingthe start relay R65 completes, at the contacts 66, a multiple circuit, including the contacts 9|, for energizing the winding ci the control relay R85 in order to cause thela-tter relay to operate shortly thereafter, it being-c1e the slow-to-operate type. Upon operating the control relay R80 completes, at the contacts 8i, a circuit for energizing' the winding of. the control relay R85 in order to cause the latter relay to operate shortly thereafter, it being of the slow-- to-operate type.

Upon operating the control relay R85 ccm- -p1etes, at the contactsr 86, a circuit for energizing the winding of the control relay R90 inorder vto cause the latter relay to operate shortly thereafter, it being of the slow-to-operate type. Upon operating the control relay R90 interrupts., at the contacts SI, the circuit for retaining operated the control relay R80. Upon restoring the ccn- 4trol relay R'effects the restoration of the control relay R85, and the latter relay enects `the restoration of the control relay R60. Upon re- "storing the control relay R90 eiiects the reoperation of the control relay R80. Accordingly, .the control relays R80, R65, and R96 operate repeatedly through the cycle described. The lower winding of the tone relay R10 is initially energized'via a circuit, including the contacts 62 and 92, the condenser 63, the tertiary winding 46 of the repeating coil 45 and the resistorv 5I; whereby the tone voltage induced in thel low-er winding of the tone relay R10 lcauses a corresponding tone to be induced by the tertiary winding 46 of the repeating coil 65 into the primary winding sections 48 and 49. Upon operating the control relay R80 interrupts, at the contacts 82, the initial circuit traced above;V and upon operating the control relay R65 recomvpletes, at the contacs 81, a point in multiple-to 4thecontacts 82 of the operated control relay R85, "in the tone circuit mentioned. lUpon operating -Ythe vcontrol relay R90 v"again interrupts, at the the contacts v82 and 92. Accordingly,.the control relays R80, R05 and R90 are effective to cause the tone Voltage generated in the lower winding of the tone relayRlU to be applied internlittentlyk .to

the tertiary winding 46 of the repeating coil 45;.

whereby a distinct intrusion tone is producedA the repeating coil 45 and applied to the telephone channel of the cord circuit 30; which intrusion tone is not only audible tothe operator` atthe position illustrated at the switchboard lill-tile P. B. X I5, but is also audible to the person at the telephone station TI in the P. B. X I0 and to the person or operator in the central ofce, thereby indicating to the operator at the position illustrated-at the switchboard in theP- B. -X ,I0 that she should restore the talk key K3] and indicatingto the person at the telephone stationTI inl the P. B. X E0 and the person Oroperatorgin the central cnice that the established telephone connection is not private at vthis time.

Normally, the operator at the position-illus,- trated at the switchboard in theP. B. X 4I0 restores the talk key X31 interrupting, at the iirst the established telephone connection private be.' tween the repeating coil 45 and the telephone channel in the cord circuit 30 inV order to render the established telephone connection private-.be-

tween the person at the telephone station TI in the P. B. X I0 and the person or operator vin the central office. Also when the talk key X31 is restored, there is-interrupted, at the third contacts thereof, the circuit; for retaining operated the start relay R65; whereby the tone relay R10 and the control relays R80, R85 and R90 restore interrupting the application of tone potential to the tertiary winding 46 ci' the repeatingcoil 45. At the'ccnclusion of the established connection, when the person at the station 'II in the P. B. X I0 disconnects the circuit forenergizing the Winding of the series relay Rittr isinterrupted causing the latter relay to restore. Likewise, rwhen the person or operatcrin the central olice disconnects, the circuit for energizing the winding of the. series relay R966` is interrupted in order to cause the latter relay to restore.v Upon restoring the series relay RIB again completes, at the contacts I6I,tlf1e circuit for illuminating the front supervisory lamp L33 indicating to the operator at the position illustrated at the switchboard in the P. B., Xl I0 that the connection involving the cord circuit 30 may be takendown. VThe operator at thepcsition `illustrated then withdraws the front plugv PBI from the line jack J I1 and the rear plug .P32 from the trunk jack J I3. When the -front plug PBI is thus Withdrawn the circuitior illuminating the front supervisory lamp L33 isl interrupted and when the rear plug P32 is thus withdrawn the circuit for energizing'in series the lower'winding of the control relay RI50 and the lower winding of the sleeve relay RMB is A.interrupted, causing the relays mentioned tc restore. At this time the established connectionyinvolving the trunk II extending to the central oiilce and the line I5 extending to the telephone station TI is released and the cord circuit 30 is idle and available for further use.

During the established connection via the cord circuit 30 between the trunk II extending to the centralcfflce and the line I5 extending to the telephone'staticnTI, should the operator at .the

`suzvitchboard reoperate the talk key K3? in order again to complete a connection between the operator telephone circuit 40 and the telephone Schannel in thecord circuit 30, .the previously 'traced circuit for operating the start relay R65 telephone .station TI in the P. B. X I0, the

linecircuit I6 is governed to illuminate the line laznpLISin order to indicate the presence of the line call-waiting Vtofbe answered. Now assumingrthat the operator at the position illus- -trated atthe switchboard in theP. B. X it is idleand is'to answer the call utilizing .the idle cordeircuitt, theoperator inserts the .front plug P3I1into the link jack J I1 extending Ato lthe-linecircuit I8, and the talk keyKB' is operated. When the vfront plug P3I is inserted into the line jack JI'|,'the line circuit is governed in order to exinguish the line lamp' I8 indicating that the call on the line I has been answered at this time. Also, a circuit, including thesleeve of the line jack J I1, the sleeve of the front plug P3I and the contacts |46, is completed for-operating the sleeve relay RI'20. Further, currentis supplied to the telephone station TI via the upper and lower windings of the battery supply relay R|30 and the winding of the. series relay RI60. Specifically, ground potential is connected via the contacts I 4| andv upper winding of the batterysupply relay R130 and the contacts I'|I to the tip of the front plug PSI; and battery potential is supplied via the resistor |54, the contacts |44, the lower winding of thebattery supply relay RI30, the winding ofthe series relay RISO and the contacts |14 to the ring of the frontvplug PSI; and the connection is extended `from the front plug'P3l via the line. jack J I1, the line' circuit I5 'and' the line I5 to the telephone station` TI. Accordingly.; the VwindingV of the series relay RIGI! and the upper. and lower windings of the battery supply relay `15H30 areV energized, causing these relays to operate.

Further, ground potential suppliedto'the sleeve 'of' the front plug PSI completes a circuit, including'the contacts |03v and III, for illuminating the i rear supervisory lamp L34, indicating that 'the call has-not been extended at this time. Accordingly, at this time a telephone connection is lcompleted between thetelephone station TI and the operator telephonecircuit l0 soV that the operator at the position illustratedfat the switchboard in the B. PJXSII) mayconversewiththe person at-the calling telephone L station TI and llearn the required extension of .the call.

Now assumingthat the call'initiated at the vcalling telephone 'station TIV and answered at'the vposition illustrated a-t the switchboard in the P. B. X I0 is tobe extended to another telephone station in the P. B.. vX .|0, suchyfor example, as the called telephone station T2`,.the.operator'in serts the rear plug P32 into the line jack J22,

assuming that .the telephone station T2 isidle at this time, as indicated by the extinguished line lamp L23. At 'th-istime' the operated sleeve relay RI interrupt-sat the contacts .|2:| and |24, Y

the previously traced direct connection between the upper and lower windings of the battery supplyl relay RI'30 #andthe tip andfthe ring of the rear plug P312; and completes, at. thecontacts |22 and |23, a path for bridging the upper'and' lower windings of the battery supply relay RI I0 via the contacts IUI and |06 to the tip and the ring of the rear'plug P32. The operator thenoperates the ring trunk and station key K3B, completing, at the second contacts thereof, a circuit for opera-ting the ring relay RI 00. Upon Voperating the ring rel-ay R|00 interrupts, at the contacts |0I and |06, the connection between the tip and the ring of the rear plug P32 and the telephone channel in the cor-d circuit and completes, at ythe contacts I02 and |05, Ia path, including the first and third contacts oi the ring vtrunk and station key KSG, for connecting ground potential and the ring conductor CI6'5 respectively to the tip and the ring of the rear plug P32 and, consequently, to the tip and the ring of the line jack J22; whereby ringing current is projected over the line 20v to the telephone station T2, operating the ringer therea-t. The operator then restores the ring trunk and station key K36 in order to interrupt, at the second contacts thereof, the circuit for energizing the winding of .the ring relay R|00, causing the latter relay to restore shortly thereafter, it being of thev slow-t0- release type. Upon restoring the ring relay R|00 interrupts, at the contacts |02 and |05, the path for projecting ringing current over the line 20; and recompletes, at the contacts |0I and |06, the connection between the tip and the ring of the rear plug P32 and the telephone channel in the cord circuit `3l).

When the call is answered at the telephone station T2, a circuit substantially identical to that previously traced is completed for supplying battery current via the upper and lower windings .of the battery supply relay ARI I0 to the telephone instrument Iat the telephone station T2; and a three-way telephone connection is completed involving the per-son at the calling telephone station Tl, the person at thecalled telephone station T2, and the `operator position illustrated. At this time battery current is supplied to the calling telephone station TI via the upper and. lower windings of the battery supply relay RIBI); and battery current is supplied to the called telephone station T2 viathe upper and klower windings of Ythe battery supply relay RI I0. Also, the two sections of the telephone' channel in the cord circuit 30 respectively extending to the front plug P3I and to the rear plug P32 are coupled by the two condensers |28 and |29A for communie-ation therebetween.

Moreover, when. the call is answered at the telephone station T2, the battery supplyv relay R|i|0 operates, interrupting at the cont-acts I|I, the circuit for illuminating the rear supervisory lamplll, indicating that the call has been answered at the telephone station T2. Also, the battery supply relay RI I0 completes, at the contacts 2, a circuit, including the contacts |25, |53 and the third contacts of the talk key K3'I, for operating the start relay'liv in the tone circuit 60; whereby the intrusion tone is impressed upon .the telephone channel in the cord circuit 30 for the purpose previously explained. The operator vat the position illustrated at the switchboard in` the P. B. X l0 then restores the talk key 31, interrupting, at the lrst and second contacts thereof, the connection between the operator telephone circuit and the telephone channel in the cord circuit 30; and interrupting, at the third contacts of the talk key K31, the circuit for Yretaining operated the start relay R65. At this time an established connectionis completed between the calling telephone station TI and the battery potential in the trunk circuit I2.

called telephone station T2, excluding the operator telephone circuit 40 at the operator posirtion illustrated at the switchboard in the P. B. X I0.

At the conclusion of the established connection when the person at the station TI disconnects, the circuit for energizing the winding of the series relay RIGD in series with the upper and lower` windings of the battery supply relay RIS!) is ine terrupted in order to cause the relays mentioned to restore. telephone station T2 disconnects, .the circuit for Likewise, when Y the person atl 'the energizing in series the upper and lower wind` supervisory lamp L34, indicating disconnection by the personl at the telephone station T2. The operator then takes the connection down by withdrawing the front plug P3I from the line jack J II and by withdrawing the rear plug P32 from the line jack ,I2-2. v thus withdrawn from the line jack J Il, the multiple circuits for illuminating the front supervisory lamp L33 and the rear supervisory lamp' When the front plug P3| is L34 are interrupted. At this time the established d connection involving the calling telephone sta-` tion TI and the called telephone station T2 is released and the cord circuit able for further use.

is idle .and` avail- During the established connection via the cord y,

circuit 3D between the line I5 extending to the telephone station TI and the line 20 extending to the telephone station T2, should the operator at the switchboard reoperate the talk key K3'I in order again to complete a connection between the operator telephone circuit 40 and the tele-v,

phone channel in the cord circuit 3i), the pre# viously traced circuit for operating the start relay R in they tone circuit 6|? is recompleted at the third contacts of the talk key K3'I; whereby the intrusion tone is again impressed upon the,r

telephone-channel in the cord circuit Safor the,v

purpose previously explained. l

New assuming that the call initiatedat the calling telephone station TI and answered at the position illustrated at the switchboard in the P. B. X Ill is to be extended to the central office, the operator first selects an idle trunk, such, for example, as the trunk II, and inserts the rear plug P432 into the trunk jack J I3, the trunk lamp.`

LI 4, being. extinguished at this time, .indicating the idle condition ofr the trunk lI I. When the rear plug P32' is thus inserted intothe trunk jack J I3,.the trunk circuit I2 is governed to illuminate the trunk lamp LM in order] to indicate the busy conditionof the trunkv I I at this time. Also, a series circuit is completedfor energizing the upper and lowerr windings of the control relay RI 5U and the lower winding of the sleeve relay RUM);V this circuit extending from ground potential by way of the lower winding of the sleeve RMD, the upper and lower windings of the control relay RI5B, the contacts I 04, the sleeve of the rear plug P32, and the sleeve of the trunk jack J'I3 to When this series circuit is completed, the control relay R|5D operates to complete, at the contacts ISI,

a path for short-circuiting thel upper winding 10i.' thereof, in order to reduce the resistance in the series circuit for energizing the lower winding of the control relay RISE) and the lower winding of the sleeve relay RMU; whereupon thev control relay'RIEO is retained in its operated position andthe sleeve relay-RIM) operates. Upon operat'ing, the sleeverelay RII-13 interrupts, at the vcontacts MI and IM, the previously traced cir cuit for'supplying batterycurrent via the upper -andxlower windings of the battery supply relay RIB!! and the front plug P3| to the calling telephone station TI; whereby the battery supply relay RI 3|) and the series relay RI 6B restore. Upon restoring, lthe series relay R|60 completes, at the contacts IGI, the previously traced circuit for illuminating the front supervisory lamp L33. Also, upon operating, the sleeve relay R|4Ii prepares, at the contacts |42 and "|43, a path, including the condenser |49 and the contacts I2I, |24, IUI and |06, for bridging the upper winding of the sleeve relayv RIMlvia the upper and lower windings of the battery supply relay RI3U, acrossl the tipand the ringof the reary plug P32.` Further, upon operatingthe sleeve Vrelay RIM) interrupts, atthe contacts |46, thecircuit for retaining operated lthe/.sleeve relay .fRIZG andl interrupts, at the contacts |48, the previously traced circuit for illuminating the Vrear supervisorylamp L3II.y Upon restoring, the sleeve relay RI20 com- I pletes, at the contacts |2I and. |24, the previously traced path for bridging the upper winding of the sleeve relay RMU via the upper and lowery windings of the battery supply relay RI30, across the tip'and the ring of the rear plug P32.

The illuminated front supervisory lamp'L33 indicates. that the present call extended to the central oce via the cord circuit 3|) has not been answeredat this time. 1

The operator then operates the ring trunk and station key K36, completing, at the vsecond contacts thereof," the' circuit for operating the ring relayRIQG. Upon operating, the ring relay RIUD completes, at the contacts |93, a local holding circuit, including the resistor |54 `and the contacts |45, for energizing the lower winding of the control relay RI 53 in series with the lower winding of the sleeve relay RMD; and interrupts, at Y the contacts IEM,l previouslyftracedioriginal cir-r l cuit for energizing'thelower winding of the control relay' RIESE:` in series vwith the lower winding" of the sleeve relay RI 40. Also, the ring relay RIM! interrupts, at the contacts IUI and IBB, the

connection between the tip and the ring of the rear plug P32 and the telephone channel in the vcord circuit 33j and completes, at the contacts I @2 and |05, 'a path, including the rst and third contacts of the ring trunk and station key K36,

for connecting ground lpotential and the ring conductor CIE5, respectively, to the tip andthe ring of the rear plug P32 and, consequently, to

the'tip and the ring of the trunk jack'y J I3; whereby ringing current is projected over the trunk II tothe central oiiice. The operator then restores the ring trunk and station key K36 in order to effect the restoration of the yring relay R shortly thereafter, the latter relay being of the slow-to-release type. Upon restoring the ring relay RI Il!! interrupts thepath for projecting ringing current over the trunk II and recompletes the connection between the tip and the ring of the rear plug P32 and the telephone channel in the cord circuit 3|). f

When the call is answered in the central of- V nce, battery current thereinis supplied via the line conductors of the trunk II, the trunk cir- I1," cuits I1; the'Y tin armi-the ring of 'the trunk; jack.' Ti-6,; tlieitip 'andi-the. ring: or. the rear: plug P32; the 'contacts'..l'tr lzlli,V IZ'I, IZA; the:V winding of. th'e'f series?. relay. Billing, the r contacts: I 'I. I ITM) the.. tip'. and the'. ring; of' the'. fronti .plug P31, the' ti'p' andth'ering `of the line jackJ'IiI, .the-.line-.circuit I 6; and the'. lineaconduct'orsf of'. the:v te'elephone` liner Itotlrecallin'g' telephoneV station TI. Whenv .thisi circuit 'is thus'-completed, theseriesrelay R'Izr'operates; also.' ar telephone connection. is completed; between. the .operator telephone. circuit l 'andf'the channel in. the'. cord. circut.- 30 so that' theoperatorkat theipositiorn illustrated at the. switchboardzimth'e P'; Bf. X. ItII may converse. with thelpersonat thef-calling.telephone':.station TI and with the` person'. or opera-torin. the.centr.al'. office...

Upon-operating the: series. relay.' RIBU inter.'-v rupts, at: the contacts: LEI, thecrcuit forv illumisv mating the front.supervisory'lamp.L3%, indicating. y

thatlthe.I call'h'asz beenanswered in the central office. Furthe1i, the. series relay" R; Iz" completes',

nection between' the operator.A` telephione circuit.

i6 and the!telephoneY channelintheYcord` circuiti Bit; andzinterrupting,1at thathirdzcontacts there- 012;, thez'circuit. for retainingA operated the; start4 relay R'. At thistirne anfestablished` connecition is completed between the; callingtelephone: station: TI in'- the/P; Infandthe, called telephone stationf or operai'ior'switchboard in the central: oil-iceI excluding the. operator telephone circuit at the operator-position illustrated at.

theswitchbcardfinthe E: ELX Ill.

.Atsthe' conclusion of: 'the established.A connection-whenA the person; at the telephonerstati'en TVI: injtlie-P:v B.: X'I.- disconnects,y the circuit for retaining; operated the? seriesrelay RI 60 isa inter`rm ruptedf. Likewise; when the personi onoperator inthe centr-al cnice disconnects, the. circuit' for retaining. operated' therseries-relay- R'lii' is int-er.- rupted. Upon.Y restoring thef series relay Rlil completesv at the contactsE I8I^, thecircuit forA illuminating: the front' supervisory. lamp. L53 indicating. to the operator: at' theposition illus-A tratedgat-therswitchboardfinthefP; B. Xl. I$=that ff thel connection-involving the.V cord circuit 3B( may be: taken. down.. The;A eperator at theposition illustrated then .withdraws the front plug P34 from. the line -j ack JM and the-rear plug-1332v from thetrunk-Jack. Ji3,; interrupting the circuit for illuminating the. 4front:supervisorylamp L33 and eicctingfthe restoration ofthe sleeve-relay RME; and the. control relay Riflin: the-manner previously explainede Atrthis 'time-the established.

'connection involcvingrthe trunk H: extending to:

thecentral'oiceand the'line I5 entendinggto the telephone station TI isfreleased andthe cord circuit 3i?. isfidleandfavailab'le for fur-ther use;

During the established connectionl via. the cordcircuitzvbetweena-the. trunk IIA extendingl to the central oiiceand the'line.' 'I5 extending to' the telephone station TI should the-operator at the.`

switchboard reoperate theta/lk key-:KSJ in order again to complete .aY connection between thev operator telephone'l circuit iwf and1 the telephone` channel. inL the; 4cordl circuit.' 3.9,.. the. previously tracedl circuit; for: operating the'l toneY circuit @iii recompl'eted 'Ii/'hereby' the. intrusion teneis againi impressed upon the telephone channel'. in thc-Y yc ordi z circuit. 35i; for. the purpose4 previously explainedz.

Now. assumefthati a .connectionihas b 'eeriasetupr involving; ther-trunk. I-'.I extending-to the centralofca and?. theline I 5r extending; to` the'. telephone stationilTI: utilizing; a cord circuit, not' showin eith'er at fthe Yoperator position illustrated er at.' another operator. position, not shown, a-tjtheswitchboardl,tandfthat the opera-tor at the switch?- boa-rdf'imthel?. B. X-Iilv endeavors to listenin! uponA the` establishedconnection utilizing the idle. cordI circuitv Ell. In orderl to:` attempt this objectivetheA operator at thev position illustrated may inserty the. rear. plug- P32- of. the idle corti:v circuit's, into ainultiple oi the trunkjack'Ji-3;.` In-.thisfcase the battery potentiala appearing upon.A the-sleeveoi themultipleof the trunk j ackgJiS-iisl of intermediatevaluadue tothe. previously corn,- pleted` connection via the cord? circuit, notshovvn.;

wherebyI thecircuit for. energizingin. series theupper. and lower, windings' of.A the control. releuy RIEBL and. the lawer. winding.- ot the. sleeve relay RIAII causes operation. of. the. sleeve relayv RIM`v without .eiecting operation of tlie.- control relay RI.-5i, .since the .controlrelay RIBQ iso the; mar. v

At, this` time,L in. the. event. the` talle keyK is-operatedthereis completed;..at the.

ginal, type..

thi'ri contacts, thereof-Q, a. circuia, the contacts. [ISL and I5l lor. operating the. start relay Rin the tone circuit 60;; whereby the; intrusion tone. is impressed upon. the telephone channell in the cord circuit 3G' and'conse.quently, upon the established.v connection. including, the corel' circuitr not. shown.

Alternatively in. order to attempt' this o bjjec.-

tive'. the operator at. theposition illustrated' may insert' vthe front plug P3] ofthe idle cord circuit` 30 intothe' multiple of the trunk jack J I3.. In

this.' casetlrej battery' potential' appearing upon` tl'efsleeveof; the. multiple of the trunk jack J'I'i is.

of' intermediate' value,v dueto' the previously completed' connection via'the cordl circuit, notshown; whereby the'winding of; the sleeve relay R120' is. not'I .sufficiently energized to. effect operationv thereof ,since'i't'is1 of the' marginal' type Accord.- ingly, the above' tracedcircuit for energizing the vwinding of thestartrelayiR the' tone circuit' SUffis recompleted, at'y the' third contacts' of thel talk key; K3`7I incident' to; operation thereof; whereby" the intrusion tone; is impressedlupon' the telephone channel in the cord' circuit' 32] and,

consequently; upon' the established' connection including thecordl circuit, not shown.

As"A a further' variation ofthis` attempt, the op. era-tor at' theposition illustratedV may rst insertI the front p1ugjP3 I; ofthe cord circuit. into an idleI linejack; such,v for' example', as'the line jack` J I"If, and then' insert the rear plug P32 into. the

muitipl'e'of the'. trunk jack J I 3'. In this `case when. the front plug. P31' is inserted into the idle. line.A

jackrlIT the sleeve relay. RIZU isoperated in or- A der. to completaatgthefcontacts |22 and, I-23,.the

previously .tracedpath fonbridging.. the upper'and lower windings or the batteryl supply relay RI I-.Ilacross, the tip and.- the ring vof the rear; plug.L P32.

. When. they rea-r plug P32 is-then'y inserted into the.

multiple ofu the trunk. jack J I3,` the upper and' lower` windings of,- the'battery` supply relay RI- I 9.- are bridge acrosstheline'conductors. ofi the trunk I I, whereby battery currentV is supplied via'Y the: upper.` and lower windings? oftheA battery supply relay RI lll in multiple with the central oiilce to the telephone station in the P. B. X involved in the established connection via the cord circuit, not shown; whereby the upper and lower windings of the battery supply relay RI I are energized in series circuit relation, causing the latter relay 'to' operate.v Also, whenv theY rear plug P32 is inserted into theA multiple of thetrunk jack J I3, the sleeve relay RIM) is operated and the control relay Riel) is not operated, as previously explained. Accordingly, at this time a circuit, including the contacts l53, |25, H2 and the third contacts of thetalk :key K3?, is completed incident to operation oi' the talk key X31 for operating the start relay R65 in the tone circuit 6G; whereby the intrusion tone is impressed upon the telephone channel in the cord circuit 30 and, consequently, upon the established connection including the cord circuit, not shown.

In view of the foregoing, vit will be understood that it is impossible for lthe operator'at the po-v sition: 'illustrated' at the switchboard to utilize the idle cord circuit 34D to listen in upon` an established connection completed between a telephone station in the P. B. -X--lll and the central cnice viaanoth'erc'ord 'circuitwithout causing the intrusion tone to be impressed upon the established connection, giving the presons involved therein warning ofthe unauthorized entry of the operator at the position illustrated at the switchboard in the P. B. X l0. 1 l

' Now assume that a connection has been set up involving the lines l and'Z in theP. B. X lll utilizing a cord circuit, not shown, either at the operator position illustrated or at another operator position, not shown, at the switchboard and that the operator at the position illustarted at the switchboard inthe P. B. X l0 endeavors to listen in upon the established connection utilizing the idle cord circuit 3S. In order to attempt .this'objective the operator at the position illustrated may insert the rear plug P32 of the idle cord circuit 30 into amutliple oi the line J' ack J 22. In this case the potential appearing upon the sleeve of the multiple of the line jack J 22 is of intermediate value, effecting operation of the sleeve relay Rill!) and preventi'ngcperation ci the controlrelay R150; whereby thestart relay R535v isoperated incident to operation of the talk key X3i, .for the purpose previously explained. v

Alternatively, the operator may attempt this objective by inserting the front plug P3! of the idle cord circuit 30 into the multiple of the line jack '22. In this case the potentialappearing upon the sleeve of the multiple'of'theline jack f a tone source and a cord circuit adapted to set up a telephone connection betweenrtwo of 'saidv lines or between one of said lines and'onefof-1 said trunks; said cord circuit including a ltelephone channel, a key, -meansrespcnsiveto' Opff eration of said key for connecting said telephone vset to said telephoneV channel,v a rlrstv battery supply relay,` ay second battery supply rela'y,'"a sleevev relay, a-series relay, Vmeans responsive to J22 is of intermediate value, preventing cperation of the sleeve relay R120; whereby the start relay R is operated incident to operation of the talk key K3?, for the purpose previously eX- plained.

ln view of the foregoing, it will be understood that it is impossible for the operator at the position illustrated at the switchboard tc utilize the idle cord circuit 3i) to listen in upon an established connection completed between two lines in the P. B. X HJ via another cord circuit without causing the intrusion tone to be impressed upon the established connection, giving the persons involved therein warning of the unauthorized entry of the operator at the position illustrated at the switchboard in the P. B. X l0.

In view of the foregoing, it is apparent that there has been provided in a P. B. X a switchboard including operator positions provided with cord circuits that may be utilized for the purpose 14 of setting up local calls in the P. B. X and trunk calls involving the P. B. X and a central office, which `cord circuits are-so` connected and arranged that it is impossible for theoperator atl any position at the switchboard to intrude in'any established connection without causing awarn-fr ing tone to be impressed thereon indicating such intrusion. I

While there has been described whatfis at pres-Y ent considered to be the preferred embodiment of the invention, it will be understood that' va`r" ious modifications may be made -therein,"and`it` is intended to cover in the appended claims-"all spirit such modifications as fall within the true and scope of the invention. l 'f What is claimed is: l. In a telephone system including a central cnice, a private branch exchange provided with lines and a manual switchboard, and-trunks eX- tending between saidoiiice and said'e'xchang'e, said switchboard including a telephone set and of said key for connectingrsa'id 'telephone'setto said telephone channel, a first relay controiled''A in response to the completicnof'a telephone con- A, nection via said telephone channelbetween two" of said lines, a second relay controlled in response f to the completion of a telephone ccnnectionv via said'telephone channel betweencne ofi'said lines and one 'of said trunks, a nrst'circuitgoverned' jointly by operation oi said key and control of said iirst relay for eiiectinglconnectio'n of said I tone source to said telephone' channel, land' a second circuit governed jointlyby operation 'cil said key and control of said secondarelay forA eiecting connection of said tone sourceltofsaid telephone channel.

2. In a teleDhOne system including acentralI olice, a private branchexchange providedwith lines and a manual switchboard, 4and, trunks eX-' 1 tending between said office and said exchange, j

said switchboard including a telephone. set and connection of said telephone channel to a calling one of said lines for supplying current thereto via said iirst battery supply relay in order to effect operation thereof, means responsive to answering of a call on a called one of said lines" to'which said telephone channel is connected for supplying current thereto via said second battery supply relay in order to effect operation thereof, means responsive to connection of said telephone channel to a called one oi said trunks for operating said sleeve relay, means responsive to operation of said sleeve relay for disconnecting said rst battery supply relay from said telephone channel in order to effect restoration thereof, means responsive to answering of a call on said one called trunk for supplying current thereover and via said telephone channel and said series relay to said one calling line in order to eiect operation of said series relay, a iirst circuit governed jointly by operation of said key andbyioperation of. said second battery supply relay-'for effecting; connection of said-,tonesourceto-,said-,telephone channel, and a second circuit governed jointly byoperation ofsaid key and byoperation of said series relay for effecting con-A nection of said tonesource tosaid telephonechannel.

3. In atelephone system including a centralofce,- a private branch-` exchange provided with linesand a manual switchboard, and trunks extendingl between said.- office and said exchange, said;- switchboard.4 including a telephone' set and af-'tone source and a plurality of cord circuits eachY oiwhich is adapted` to set upa telephone connection between two of said lines or between. one of said lines and one of. said trunks-g' each oi saidv cord circuits includinga telephone channel, akey, means responsive to. operation of. said key forA connectingsaid telephone: set to said .telethe. event said one trunk isy idle andY responsiveto. connection of said telephone.y channel to one. of said lines for retaining said sleeve relay, inits.restored position regardlessof the idle. or

busy-condition. of. said one line, and a circuit gov.-

. erned jointly by operation of.. said key. and by the. restored. position of said sleeve relay for effecting. connection ofsaid tone` source to said telephone channel.

4. 1n a telephone system including a centralV oice, a` private. branch exchange provided with linesand amanual switchboard, and trunks extending Ybetween said oiceand said' exchange, said switchboard including a telephone set and a tone source and a plurality ofcord circuits each of, which` is adapted toset up a telephone connection between twoof said linesor between one of said lines and one of said trunks ;v each of said cord. circuits including a telephone channel, a key, means.. responsive to operation. ci. said key for connecting" saidtelephone set to. said telephone channel, ay sleeve relay normally .occupying, a restored position,.means responsive to4 con'.- nection offsaid telephone channel to oneoi said linesfor operating said sleeve relay only in thc eventi saidv oneline is. idle andresponsive to con,-

nection of said telephone channelV to one of. said trunks.. for retaining, said sleeve relay.y in. its reeV of said cord circuits'including; atelephonechannel, a key, means responsive to-operationfof said' key for connecting Vsaid telephone-settosaid telephonechanneL; a vrst. sleeve; relay normally l,

occupying` av restored. position, means responsive-V to, connection. of said. telephone.- channel.- to: one of saidtrunks foroperatingfsaid-.iirst sleeve relay only in the event said one. trunk. is idle and responsive to connection ofsaid-.telephone channel to one of said lines for retaining'saidrst sleevey relay in its restored'- position. regardless of the idle-.or busy condition of said one-line, asecond.'V

sleeve relay normally occupying a restoredpos'b tion,vmeans responsiveto connectionA ofsaid'telephone channel to one of, saidlinesfor operating said-.second sleeve relayonly-'in the event said' one line. is'idleandi responsive to. connection of said telephonev channel; toone: oi said trunksv for retaining saidsecond-L sleeveI relayin; its: re..- stored position regardless of the idle orqbusy con-- dition of said one trunk, and acircuit governed jointly by operation. of said. key; andl by the 11e-.- stored positions:- of both. sad-A rs-t. and second;

sleeve relays for effectingl connections of: said' tone: source-to said; telephonechannel.

L. Bon-Genna.

REFER-ences. einen,

The following referencesl are of record' iny the file of this patent:`

y UNTED. STATES' P25'lZEl\I'I'S.V

Number Name. Date 1,097,760 Koltonski May-26, 1914 1,207,823 Webster Dec. 12, 191.6' 1,617,611 Wallace Feb. 15, 1927 1,783,310 Saunders .Dec. 2; 1930' 1,931,603 Darrow Oct. 24, 1933.- 2,057,864 Voss Oct.,20, 1.936 2,087,930 VossV July 27, 1937". 2,252,857 McAndrew Aug-1.9, 1941i. 2,333,140- A-l1en. Nov. 2, 19.431 2,335,481' Boswau:r Nov.; 30, 1943: 

